Low Temperature Cured Silicone Lubricious Coatings

ABSTRACT

Novel, lubricious coatings for medical devices are disclosed. The coatings provide improved lubricity and durability and are readily applied in coating processes a low temperatures that do not deform the device. The present invention is also directed to a novel platinum catalyst for use in such coatings. The catalyst provides for rapid curing, while inhibiting cross-linking at ambient temperatures, thereby improving the production pot life of the coatings.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of co-pending U.S. Application16/697,222 filed Nov. 27, 2019, which application claims the benefit ofU.S. Provisional Application No. 62/773,102 filed Nov. 29, 2018, thecontents of which is incorporated herein by reference in its entiretyfor all purposes.

This application is related to U.S. Non-Provisional Application No.16/697,223 (Attorney Docket No. ETH6058USNP1), being filed concurrentlyherewith and having a common assignee the contents of which are hereinincorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

The field of art to which this invention pertains is silicone-basedlubricious coatings, in particular, silicone-based lubricious coatingsfor use on medical devices.

BACKGROUND OF THE INVENTION

Lubricious coatings are typically required for implantable or insertablemedical devices such as sutures, hypodermic needles, surgical needles,catheters, and cutting devices that contact tissue. The primary purposeof such coatings is to ease the penetration or insertion of the deviceinto and through tissue, thereby facilitating a procedure.

A number of conventional, biocompatible lubricants have been developedfor such applications, and they are typically silicone (e.g.,polydimethylsiloxane) or silicone-containing coatings. For example,condensation-cured silicone coatings are known to be useful aslubricious coatings on medical devices. Such coating formulationscontain amino and alkoxyl functional groups, which can be cured(cross-linked) at relatively low temperatures and high humidity levels.It is also known to use an aminopropyl-containing silicone as alubricious coating for syringe needles. Those coatings use anepoxy-containing silicone as a cross-linking agent and may have improvedpenetration performance with multiple penetrations. It is also known toutilize thermoplastic polymers such as polypropylene (e.g., in powderform) in blends of silicone solutions to improve the mechanicalproperties of the resulting coating layers. The polypropylene powdersmay increase the durability of silicone needle coatings withoutsacrificing lubricity. Most of the known and conventionally usedsilicone coatings listed above require a lengthy thermal curing stepafter application, which is quite often unsuitable for rapid, high speedproduction processes.

Attempts have been made to improve coating cure times including rapid UVcurable silicone lubricious coatings that can be cured rapidly (<10seconds) on a medical device, such as needle, after UV light exposure.However, the potential hazard of certain UV curable components typicallycontained in such coatings may provide cause for concern.

Karstedt of GE Silicone invented a highly active platinum catalyst forhydrosilylation at the beginning of the 1970’s (U.S. Pat. No.3,775,452). The “Karstedt catalyst” is highly active at ambienttemperature, and this quality makes it difficult to use in mostcommercial silicone coatings without the addition of an inhibitor.Several other platinum catalysts had been subsequently inventedattempting to address this problem. For example,platinum-cyclovinylmethylsiloxane complex was made immediately after theinvention of the Karstedt catalyst (U.S. Pat. No. 3,814,730), and thiscatalyst is purported to provide longer production process pot life fora vinyl/hydride reactive coating solution mixture.

Commonly assigned US Pat. Nos. 9,434,857 and 10,441,947 describe novel,lubricious coatings for medical devices. The coatings provide improvedlubricity and durability, and are readily applied in conventionalcoating processes. These patents are also directed to a novel platinumcatalyst for use in such coatings. The catalyst provides for rapidcuring, while inhibiting cross-linking at ambient temperatures, therebyimproving the production pot life of the coatings. A limitation of suchcompositions is that they are not suitable for coating of polymericmaterials that would be deformed due the elevated temperatures (e.g.,above 160 C) required for the compositions to be cured to form coatings.

In order to be useful on medical devices such as surgical needles andsutures, it is critical that lubricious silicone coatings be durable andeasy to apply in a uniform, consistent manner. A surgical procedure inwhich tissue is approximated or closed with surgical sutures typicallyrequires multiple passes of the surgical needle and suture throughtissue. Ease of penetration over multiple passes through tissue willmake the surgeon’s job easier and this will likely result in a bettertissue repair or closure. The patient will benefit not only by enhancedhealing and superior outcome, but also by a faster procedure resultingin a shorter time for possible exposure of the wound or opening topathogens in the environment, and also requiring a shorter period oftime that the patient is under general anesthesia, when anesthesia isrequired.

Some medical devices such as surgical needles are typically manufacturedin high speed production processes. For example, U.S. Pat. No.5,776,268, incorporated by reference, discloses such processes. Afterthe needles are formed and shaped (typically from wire stock), thein-process needles are cleaned, and the needles are coated withlubricious coatings in a conventional manner such as by dipping,spraying, brushing, etc. After application of the coatings in a uniformmanner to substantially coat the exterior surfaces of the needles, theneedles are then moved into appropriate curing equipment, such as anoven, for a coating curing process wherein energy (e.g., thermal) isprovided to cure the silicone coatings.

Silicone coatings are typically prepared at the manufacturing site bymixing the silicone polymer components with a suitable catalyst andsolvents. Such coatings and catalysts, especially when of medical gradefor use on medical devices, are expensive and typically have what isconventionally known in this art as a short “pot life”. The term potlife, as conventionally used in the art, has the meaning that thesilicone coatings when mixed with catalyst and ready for application ina coating process typically have a limited amount of time in which theyare useful because of cross-linking that occurs at ambient conditions inthe production facility. Such short pot life can result in a number ofknown problems, including for example, premature curing, leading to aviscosity increment of the coating solution during the time of itsusage. This will typically cause inconsistencies in the resultingcoating on the surface of the medical device, resulting in both visualand performance deficiencies.

There is a need in this art for improved silicone coatings for medicaldevices that have improved lubricity and durability for multiple passesthrough tissue. There is also a need for improved catalytic compositionsand silicone coatings that have improved cure times without sacrificinglubricity and durability, which do not contain potentially harmfulingredients and are capable of being applied under conditions that donot deform the device to be coated such as sutures and other polymericdevices.

There is a further need in the art for improved catalysts for siliconecoatings that provide for rapid curing when exposed to heat but whichare relatively stable in a silicone coating solution over time atambient conditions and for extended periods of time in typicalproduction environments.

SUMMARY OF THE INVENTION

Accordingly, novel catalytic compositions and lubricious siliconecoating compositions are disclosed.

In one embodiment, the coating compositions contain a firstcross-linkable silicone polymer having reactive functionalities, asiloxane cross-linking agent, and a silica-containing composition withmay be added as a separate component, but more preferably contained inthe cross-linkable silicone polymer. The coating compositions may alsocontain a platinum catalyst.

Another aspect of the present invention is a medical device having asurface, wherein at least part of the surface is coated with theabove-described novel silicone coating composition.

Yet another aspect of the present invention is a method of coating amedical device with a silicone, lubricious coating composition. In thenovel method of coating the medical device, a medical device is providedhaving a surface. A lubricious silicone coating is applied to at leastpart of the surface. The coating composition contains a cross-linkablesilicone polymer and a silica-containing composition which may be addedas a separate component, but more preferably contained in thecross-linkable silicone polymer. The coating also contains a siliconecross-linking agent and a catalyst.

Still yet another aspect of the present invention is a novel platinumcatalyst for use with cross-likable silicone coatings. The catalystconsists of a platinum complex having the following formula:

A further aspect of the present invention is a method of curing across-linkable silicone polymer containing coating solution using theabove-described catalyst.

These and other aspects and advantages of the present invention willbecome more apparent from the following description.

BREIF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an NMR peak comparison of the Karstedt Catalyst compared withthe NMR peak of the novel catalyst of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The terms silicone and siloxane are conventionally used interchangeablyin this art, and that usage has been adopted herein. Furthermore, asused herein, the term “ambient temperature(s)” is intended to describetemperatures from about 20 to about 25 C.

Lubricious Coating Compositions

One aspect of the present invention is directed to novel lubricioussilicone coating compositions which are particularly useful for coatingsurfaces of medical devices such as surgical needles and sutures andother polymeric medical devices.

In one embodiment, the compositions include a mixture of across-linkable siloxane polymer and a silica-containing compositionwhich may be added as a separate component, but more preferablycontained in the cross-linkable silicone polymer, a conventionalsilicone cross-linking agent, and a platinum catalyst. The siliconepolymer components are blended with conventional aromatic organicsolvents, including, for example, xylene and aliphatic organic solvents(such as, for example, hexane, heptane or its commercial derivatives) toform coating solutions or compositions. Other solvent suitable forcoating solution includes and not limited to low molecular weightsiloxane, e.g., hexamethyldisiloxane.

The cross-linkable siloxane polymers useful in the coating compositionsof the present invention will have reactive functionalities or terminalfunctional groups, including but not limited to vinyl terminated,hydroxyl and acrylate functional groups. The cross-linkable siloxanepolymers that can be used in the lubricious coatings of the presentinvention preferably include vinyl terminated polydialkylsiloxane orvinyl terminated polyalkyarylsiloxane. Examples include but are notlimited to the following vinyl terminated siloxane polymers:polydimethyl siloxane, polydiphenylsilane-dimethylsiloxane copolymer,polyphenylmethylsiloxane, polyfluoropropylmethyl-dimethylsiloxanecopolymer and polydiethylsiloxane. It is particularly preferred to usevinyl terminated cross-linkable polymethyl siloxane.

The cross-linking agents that can be used in the coatings of the presentinvention include conventional silicone cross-linking agents such as,for example, polymethylhydro siloxane,polymethylhydro-co-polydimethylsiloxane, polyethyhydrosiloxane,polymethylhydrosiloxane-co-octylmethylsiloxane,polymethylhydrosiloxane-co-methylphenylsiloxane. One preferredconventional catalyst for use in the coatings of the present inventionis polymethylhydro siloxane. Precise control of cross-link density inthe coatings of the present invention is achieved by precise control ofthe ratio of non-cross-linkable silicone polymer (e.g.,polydimethylsiloxane) to fully cross-linked polymer. The fullycross-linked polymer is formed by a reaction between the functionalizedcross-linkable polymer and the cross-linking agent, for example, avinylsilylation reaction between vinyl-terminated polydimethylsiloxaneand polymethylhydrosiloxane optionally in the presence of a platinumcomplex catalyst. The ratio between non-cross-linkable polymer, e.g.,polydimethylsiloxane, and fully cross-linked polymer is sufficientlyeffective to provide structural reinforcement to the resultinginterpenetrating polymer networks, and is typically between about 0.1wt./wt. and about 9 wt./wt., preferably between about 0.40 wt./wt. andabout 4.0 wt./wt. (weight of cross linker against weight of vinylterminated polydimethylsiloxane) The vinyl-terminated cross-linkablebase polymer, e.g., polydimethylsiloxane base polymer, useful in thecoatings of the present invention will have a molecular weight of fromabout 9000 and about 400,000 and preferably from about 40,000 to about100,000. Examples of this polymer include but are not limited to: GelestProduct Code No. DMS-V31, DMS-V33, DMS V-35, DMS V42, DMS-V46, DMS-V52,etc., available from Gelest, Inc., Morrisville, Pa. 19067. The typicalmolecular structure of vinyl terminated polydimethyldisiloxane is thefollowing:

wherein n is defined by the molecular weight.

The molecular weights of the silicone polymers used wherein can beestimated based on the relationship between viscosity and molecularweight (page 11, SILICONE FLUIDS: STABLE, INERT MEDIA ENGINEERING ANDDESIGN PROPERTIES, Catalog published by Gelest, Inc. 11 East Steel Rd.Morrisville, PA 19067). Using A.J. Barry’s relationship for molecularweights (M) >2,500 correlating the kinematic viscosity µ expressed incentistokes (cSt) at 25 C, the molecular weight M of silicones can beestimated as follows:

log μ_(cSt) = 1.00 + 0.0123M^(0.5)

(as published by A.J. Barry in the Journal of Applied Physics 17, 1020(1946))

The cross-linkable siloxane polymer forms the matrix phase of thecoating on surface or surfaces of a medical device. Vinyl terminatedpolydimethylsiloxane reacts with polymethylhydrosiloxane cross-linker inthe presence of platinum catalyst under appropriate conditions; thevinyl terminated polydimethylsiloxane linear polymers are fullycross-linked to each other as the result of this reaction. The amount ofpolymethylhydrosiloxane cross-linker is in large stoichiometric excesscompared to vinyl terminated polydimethylsiloxane base polymer. It isbelieved that the extra SiH functions in the cross-linker react with theOH functions on the surface of the medical devices, e.g., polymericsutures, to form Si—O—C bonds at elevated temperature or in the case ofsteel needles, to form Si—O—Fe bonds. Covalent bonds thus createdbetween the silicone coating and the device, as the result of thisreaction, result in the adhesive attachment of the coating to thedevice’s surface.

The polymethyhydrosiloxane cross-linkers, or cross-linking agents, usedin the practice of the present invention will have a molecular weightbetween about 1000 and about 3000, and preferably between about 1400 andabout 2100. An example of this polymer cross-linker includes, but is notlimited to, Gelest Product Code No. HMS-991, HMS-992, available fromGelest, Inc., Morrisville, Pa. 19607. The typical molecular structure ofthe polymethylhydrosiloxane cross-linker is the following:

wherein n is defined by the molecular weight.

Polymethylhydro-co-polydimethylsiloxane can also be used as cross-linkeror cross-linking agent in the novel coatings of the present invention.Examples of this polymer include, but are not limited to, Gelest ProductCode No. HMS-301, HMS-501. The molecular weight of this siloxane polymercross-linking agent will typically be between about 900 and about 5,000,and preferably about 1,200 to about 3,000. The typical molecularstructure of polymethylhydro-co-polydimethylsiloxane cross linker is thefollowing:

wherein n and m are defined by the molecular weight.

Silica-Containing Compositions

As used herein, the silica-containing compositions described for usewith this invention include silica materials as a separate component(such as surface treated silica) or from commercially availablecompositions that contain silica in a cross linkable silicone polymermixture.

As a separate component, silica is incorporated into the coatings ofthis invention to improve its mechanical properties and create some formof friction to ensure knot security for the suture. Hexamethyl silylsurface treatment is needed for the silica filler to enable itscompatibility to the polysiloxane polymer matrix which prevents phaseseparation in the coating solution. An example of treated silicaincludes hexamethyldisilazane treated silica i.e., trimethyl silylsurface treated silica filler (Gelest SIS6962.0).

In the case of silicone polymers already containing silica, these may beobtained from commercially available sources such as silica-containingcomposition selected from reactive silica-containing silicone basesincluding HCR (high consistent rubber) bases and LSR (liquid siliconerubber) bases, preferred are LSR bases. Other commercial examples ofthis material include and is not limited to Wacker 401-10, 401-20,401-40 base; and a liquid silicone rubber base, a commercial example ofthis material includes and is not limited to Bluestar Silbione LSR 4370base. These type of commercial silicone rubber bases are prepared bymixing a surface-treated silica filler with various molecular weights ofvinyl terminated polydimethylsiloxane polymer. In-situ surface treatmentmay be performed during the mixing process to improve the compatibilitybetween filler and polysiloxane polymer.

Catalyst

Bruce Karstedt of GE Silicone invented a highly active platinum catalyst(the “Karstedt catalyst”) at the beginning of the 1970’s (U.S. Pat. No.3,775,452). Vinyl-terminated polydimethylsiloxane can react with apolymethylhydrosiloxane cross-linker in less than one minute at ambienttemperature with as little as 10 ppm of the Karstedt catalyst. It istypically difficult or impossible to use this catalyst in conventionalneedle and suture manufacturing processes because of its high rate ofcatalytic activity, and since the economics of conventional productionprocesses ideally. Typically require up to a one week pot life for thefully catalyzed silicone coating solution for needle coating process andone shift (8 hr) pot life for suture coating process. The novel fastcuring platinum catalyst of the present invention has been developed toaddress this issue, and the resulting mixtures of this novel catalysttogether with the cross-linkable silicone polymers of the presentinvention, e.g., vinyl-terminated polydimethylsiloxane andpolymethylhydrosiloxane, with silica fillers can be stable at ambienttemperatures for 8 hours. The cross-linking reaction between thecrosslinkable silicone polymer and the cross-linking agent, for example,vinyl-terminated polydimethylsiloxane and polymethylhydrosiloxane, inthe presence of the novel catalyst of the present invention can beswitched on in less than 30 seconds at moderate elevated temperature(i.e., 70 - 110 C). The novel catalyst of the present invention isprepared by reacting the Karstedt catalyst with vinylcyclohexanolaccording to Scheme 1 as seen below. The novel catalyst of the presentinvention provides greater control over curing of the silicone coatingsolutions. This is conventionally referred to as “command cure”.

The novel catalyst of the present invention may be prepared in thefollowing manner. Karstedt catalyst in xylene solution is mixed with alow concentration of vinylcyclohexanol in a xylene solution at ambienttemperature for a sufficiently effective time to complete the reaction,e.g., a half an hour, and completion of the reaction is indicated by achange of the color of the reaction mixture, from clear to light brown.

The resulting catalyst solution containing the novel catalyst of thepresent invention is ready to use in the preparation of the lubriciouscoating solutions of the present invention. The formula of the resultingplatinum complex catalyst (platinum divinyltetramethyldisiloxanecomplex) is:

It should be noted that the resulting catalyst reaction mixture willcontain a small amount of the reaction productdivinyltetramethyldisiloxane. This component does not affect thecatalyst and is a low boiling point component that is rapidly boiledoff. Accordingly, purification of the catalyst mixture to removedivinyltetramethyldisiloxane is optional, and it is believed that itspresence will not affect the cross-linking reaction of a cross-linkablesilicone polymer. The novel catalyst of the present invention isinhibited at low or ambient temperatures and activated at higher orcuring temperatures, that is, the catalyst is inactivated at lower orambient temperatures and activated at higher or curing temperatures.This allows for command cure (command cure catalytic action) of thecross-linkable components in silicone coatings to rapidly form coatingfilms at desired curing temperatures and provides for long pot life andsuitable for suture coating processes.

Solvent and Coating Mixing Procedure

The above silicone polymers and novel platinum catalyst are dispersedinto low boiling point organic solvents to form the lubricious coatingsolution. Low temperature aliphatic solvents are used for the siliconedispersion. Aromatic solvents and hexamethyldisiloxane are commonly usedfor silicone dispersion. Typical examples include, but are not limitedto, pentane, heptanes, hexane and their mixtures. The organic solventsare added at a concentration sufficient to allow effective blending ofthe silicone polymer components into a homogeneous coating solution. Thetotal solvent concentration is from about 80 wt.% to about 99 wt.%, andis and is more typically from about 85 wt. % to about 93 wt. %,depending upon the coating thickness requirement. Those skilled in theart will appreciate that the coating thickness can be engineered bychanging the solids content of the coating solution.

The sequence of the addition of components is important. The typicalcoating composition is prepared in the following manner. In the casewhen the silica is added as a separate component, the vinyl terminatedpolydimethylsiloxane is dispersed into the first solution such ashexamethyldisiloxane together with surface treated silica for up to twohours until fully homogeneous (solution 2). Heptane is then added(solution 3) and further mixing for one hour prior to the addition ofpolymethylhydrosiloxane cross linker. The solution is fully blended forone more hour after all of the catalyst is added as the final component

In the following paragraph, the wt. % is the wt. % of total solidcontent in the coating solution. The novel coating compositions of thepresent invention will contain sufficient amounts of the polymericcomponents, silica-containing composition, cross-linking agent,catalyst, and solvent to effectively provide a silicone coating havinghigh lubricity and durability, a long pot life, and suitable forapplication in conventional coating processes using conventional coatingequipment.

Typically, the amount of the silica in the coating solution will beabout 5 wt. % to about 40 wt. % (total solids), more typically about 10wt. % to about 30 wt. % (total solids), and preferably about 15 wt. % toabout 25 wt. % (total solids). The amount of the cross-linkable siliconepolymer will typically be about 60 wt. % to about 95 wt. % (totalsolids), more typically about 70 wt. % to about 90 wt. % (total solids),and preferably about 75 wt. % to about 85 wt. % (total solids). Theamount of the silicone cross-linking agent will typically be about 0.2wt. % to about 6 wt. % (total solids), more typically about 1 wt. % toabout 5 wt. % (total solids), and preferably about 2 wt. % to about 4wt. % (total solids). The amount of the platinum catalyst based upon thetotal solids in the novel lubricious silicone coating compositions(platinum element in total solids) of the present invention willtypically be about 0.0004 wt. % to about 0.0036 wt. %, more typicallyabout 0.0012 wt. % to about 0.0028 wt. %, and preferably about 0.0016wt. % to about 0.0024 wt. %.

The amount of organic solvent in the coating compositions of the presentinvention will typically be about 75 wt. % to about 99.5 wt. %, moretypically about 80 wt. % to about 95 wt. %, and preferably about 85 wt.% to about 93 wt. %. Those skilled in the art will appreciate that theamount of solvent present in the novel coating compositions of thepresent invention will vary with several factors, and that the solventquantity in the coating compositions will be selected to engineer anefficacious coating. The factors typically considered include the methodof application, the method of cure, the coating equipment utilized,ambient conditions, thickness, etc. It will be appreciated that each ofthe components of the coating compositions of the present invention mayconsist of blends of those components. For example, two or moredifferent molecular weight non-cross-linkable silicone polymers may beused, or two or more cross-linkable silicone polymers having differentfunctionalities and/or molecular weights may be used, etc.

Coating Process

The novel silicone lubricious coating solution of the present inventionis applied to the surface of a medical device such as a polyester sutureusing conventional coating techniques and processes and conventionalcoating equipment. An example of coating equipment can be simple dipcoating tanks and in-line convection oven for curing the coating. Thecoating can also be applied by a brushing, rolling, or spraying process.The vinyl silylation addition cross linking reaction can be completedin-line by passing through a drying oven. The curing time can be asshort as 20 seconds at 100 C, 120 seconds at 95 C or 60 minutes at 70 C.Flash cure can be achieved with the present lubricious silicone coating.

Due to the deformable nature of the polymeric medical devices atelevated temperatures, it is desirable to not exceed treatment orcoating temperatures above 120 C in the practice of this invention.Preferred coating treatment temperatures range from about 60 - 110 C,more preferably from about 90 - 100 C, and most preferably about 95 C.

Other conventional curing techniques which can be utilized with thenovel silicone coating compositions of the present invention includethermal (e.g., convection heating), ultraviolet light, plasma, microwaveradiation, electromagnetic coupling, ionizing radiation, laser, and thelike. Prior to coating, the surfaces of the medical devices will beprepared in a conventional manner using conventional processes such aselectro-polishing, oxidation, ultrasonic cleaning, plasma, coronadischarge treatment, chemical cleaning, and the like.

Test Procedures for Coating Performance

Coating performance for medical devices coated with the novelcompositions of the present invention can be tested with a variety ofconventional friction or adhesion tests. In the case of surgicalsutures, coating performance, durability and integrity may be evaluatedusing the following tests.

Ease of Passage Test

To evaluate the force of friction to pull a suture through tissue, asimple comparative test was used. The intent of the test was not toquantify an absolute number for the force of passage but to establish acomparison between suture samples.

A block of high density (approximatively 210 Kg/m3 or 13PCF)polyurethane foam, 25 millimeters thick, was used as a substrate. Aone-eyed needle was used to pull the suture through the thickness of thefoam. The end of the suture was attached to a load cell and placed in atensile tester to measure the maximum force to pull the suture. Thedisplacement speed was set at 2 inches per minute.

Knot Security Test

The knot security test consists of evaluating the behavior of a knotwhen the suture is under tension. The test is conducted in a tensiletester at constant displacement. The suture is immersed in sodiumchloride isotonic solution for 24 hours and tested wet. The knot israted as being secured (no slippage), slip and break, or slip through(no break). The maximum pull force can also be reported.

As mentioned previously above, the medical devices that may be coatedwith the novel lubricious coatings include conventional medical devicessuch as surgical needles and sutures, hypodermic needles, catheters,surgical probes, endoscopes, syringes, scalpels, cutting blades,orthopaedic implants, trocars, cannulas, and the like. The medicaldevices will be constructed from conventional biocompatible materialsincluding surgical stainless steels, PTFE, glass, alloyed steels,refractory metal alloys, memory alloys, polymers, composites comprisingmetallic and non-metallic components ingredients, combinations thereof,and the like. The biocompatible materials may include nonabsorbablematerials and bioaborbable materials.

The following examples are illustrative of the principles and practiceof the present invention, although not limited thereto:

Example 1, Platinum Catalyst (Synthesis Procedure)

6 g of Gelest SIP 6831 (2.2% platinum divinyl tetramethyldisiloxanecomplex in xylene, Karstedt catalyst) was mixed with 6 g ofvinylcyclohexanol for 30 minutes at ambient temperature and the mixtureturns into light brown color. 2 g of the mixture was submitted for ¹⁹⁵PtNMR measurement. The rest of the mixture was further mixed for 5 hoursuntil dark brown. 10 g of the mixture was diluted with 990 g oftetramethyldisiloxane for further usage in the later examples.

The evidence of the formation of the new Pt catalyst according to scheme1 rest mainly on its ¹⁹⁵Pt NMR spectroscopic identification. Karstedtcatalyst give a distinguishable peak at approximately -6124 ppm. A newpeak for the novel catalyst at approximately -6001 ppm is formed 30minutes into the mixing process as illustrated in FIG. 1 .

Example 2a, Preparation of Suture Coating Solution

5.7 g of commercial high durometer silica-containing liquid siliconebase rubber (Bluestar Silbione LSR4370base) were mixed with 0.17 gpolyhydromethylsiloxane cross linker (Gelest HMS 991) and two solvents(11.4 g hexamethyldisiloxane and 60.6 g heptane) for 1 hour prior toaddition of 1.0 g of the catalyst of Example 1. The final mixture wasstirred for 30 minutes at ambient temperature.

Example 2b, Coating of Size 2-0 Polyester Suture

1 meter of polyester suture (Ethicon 2-0 Mersilene) was immersed intothe coating solution of Example 2a for 5 seconds and cured at atemperature of 100 C for 5 minutes.

Example 2c, Coating of Size 1 Polyester Suture

50 meters of polyester suture (Ethicon 1 Mersilene) was immersed intocoating solution of Example 2a for 2 seconds and cured in an in-linecuring oven at a temperature of 95 C for 2 minutes.

Example 3a, Preparation of Suture Coating Solution

2.85 g of commercial high durometer silica-containing liquid siliconebase rubber (Bluestar Silbione LSR4370base) were mixed with 0.085 gpolyhydromethylsiloxane cross linker (Gelest HMS 991) and two solvents(11.4 g hexamethyldisiloxane and 63.5 g heptane) for 1 hour prior toaddition of 0.5 g of the catalyst of Example 1. The final mixture wasstirred for 30 minutes at ambient temperature.

Example 3b, Coating of 2-0 Polyester Suture

1 meter of polyester suture (Ethicon 2-0 Mersilene) was immersed intothe coating solution of Example 3a for 5 seconds and cured at atemperature of 100 C for 5 minutes.

Example 4a, Preparation of Suture Coating Solution

5.7 g of commercial high durometer silica-containing liquid siliconebase rubber (Bluestar Silbione LSR4370base) were mixed with 0.17 gpolyhydromethylsiloxane cross linker (Gelst HMS 991) and two solvents(11.4 g hexamethyldisiloxane and 23 g heptane) for 1 hour prior toaddition of 1.0 g of the catalyst of Example 1. The final mixture wasstirred for 30 minutes at ambient temperature.

Example 4b, Coating of Size 2-0 Polyester Suture

1 meter of polyester suture (Ethicon 2-0 Mersilene) was immersed intothe coating solution of Example 3a for 5 seconds and cured at atemperature of 100 C for 5 minutes.

Example 4c, Coating of Size 1 Polyester Suture

50 meters of polyester suture (Ethicon size 1 Mersilene) was immersedinto coating solution of Example 4a for 2 seconds and cured in anin-line curing oven at a temperature of 95 C for 2 minutes.

Control Example 1a (Silica-Free Coating) Preparation of Suture CoatingSolution

9.5 g of Gelest XG2385B (a mixture of vinyl terminated polydimethylsiloxane and cross linker polymethylhydrosiloxane) was mixed with 0.55 gof the composition of Example 1 and 30.5 g heptane for 1 hour.

Control Example 2a (Identical Composition to Example 2a, but UsesKarstedt Catalyst Instead For Pot Life Measurement)

5.7 g of commercial high durometer silica-containing liquid siliconebase rubber (Bluestar Silbione LSR4370base) were mixed with 0.17 gpolyhydromethylsiloxane cross linker (Gelest HMS 991) and two solvents(11.4 g hexamethyldisiloxane and 60.6 g heptane) for 1 hour prior toaddition of 1.0 g of the 1.0% Gelest SIP 6831 (2.2% platinum divinyltetramethyldisiloxane complex (Karstedt) in xylene) in xylene. The finalmixture was stirred for 1 minutes at ambient temperature.

Control Example 1b, Coating of 2-0 Polyester Suture

1 meter of polyester suture (Ethicon 2-0 Mersilene® suture) was immersedinto the coating solution of Control Example 1a for 5 seconds and curedat a temperature of 100 C for 5 minutes.

Control Example 1c, Coating of Size 1 Polyester Suture

50 meters of polyester suture (Ethicon size 1 Mersilene) was immersedinto the coating solution of Example 1a for 2 seconds and cured in anin-line curing oven at a temperature of 95 C for 2 minutes.

Performance Testing 1. Suture Passage Testing Size 2-0 Polyester Suture

Suture passage testing was performed on Examples 2b and 3b, ControlExample 1, Uncoated Suture and two commercial coated sutures (Ethibond®suture and Ti-Cron™ suture). Dimensions of all the sutures are the same(2-0) and the results are summarized in Table 1.

TABLE 1 Size 2-0 Polyester Suture Passage Testing Sample Wet Force (g)Dry Force (g) Example 2b 37.8 26.4 Example 3b 45.3 47.5 Control Example1b 17.5 20.5 Commercial Sample 1 (Ethibond® Suture) 81.7 56.4 CommercialSample 2 (Ti-Cron™ Suture) 77.1 60.8 Uncoated Sample (Mersilene® Suture)97.1 56.4

Size 1 Polyester Suture

Suture passage testing was performed on Examples 2c and 4c, ControlExample 1c, Uncoated Suture and one commercial coated suture (Ethibond®suture). Dimensions of all the sutures are the same (Size 1) and theresults are summarized in Table 2.

TABLE 2 Size 1 Polyester Suture Passage Testing Sample Dry Force (g)Example 2c 63.2 Example 4c 58.0 Control Example 1c 54.3 CommercialSample 1c (Size 1 Ethibond® Suture) 100.4 Uncoated Sample (Size 1Mersilene® Suture) 136.0

Referring to Table 1, one observes that substantially less force wasrequired for size 2-0 polyester suture example 2b and Control Example 1(silica-free) to pass through the test media, compared to an uncoatedsuture and conventional coated suture (Ethibond®, Tri-Cron™) which showsthat the silicone coatings of the present invention show its intendedeffect of lowering the force needed to pass the coated sutures throughthe polyurethane foam versus the commercial sutures. The observation isconsistent in Size 1 suture testing referring to Table 2. Both inventiveexamples and control samples give substantially lower passage force thanthe commercial product.

2. Knot Security Testing

Knot security testing was performed on Examples 2b, 3b and 4b, ControlExample 1, uncoated suture and two commercial coated sutures (Ethibond ®suture and Ti-Cron™ suture). Dimensions of all the sutures are the same(2-0) and the results are summarized in Table 3.

TABLE 3 Size 2-0 Suture Knot Security Testing Sample Maximum Load (lb.)Knot Security Occurrence (%) Example 2b 14.5 33 Example 3b 8.2 0 Example4b 16.0 95 Control Example 1b 1.0 0 Commercial Sample 1 (Ethibond) 16.430 Commercial Sample 2 (Ti-Cron) 15.2 90 Uncoated Sample (Mersilene)17.5 100

Knot security testing was performed on Examples 2c, 4c, and onecommercial coated suture (Ethibond ® suture). Dimensions of all thesutures are the same (Size 1) and the results are summarized in Table 4.

TABLE 4 Size 1 Polyester Suture Knot Security Testing Sample MaximumLoad (lb.) Knot Security Occurrence (%) Example 2c 38.4 90 Example 4c38.0 100 Commercial Sample (Size 1 Ethibond) 26.3 50 Control example 1c1.8 0

Referring to Table 3, one observes quite surprisingly that the knotsecurity performance of Example 2b is comparable to commercial coatedpolyester suture (Ethibond®), while the conventional silicone coatedsuture (Control Example 1) lost all of the knot security.

Referring to Table 4, both inventive examples give better knot securityperformance than the commercial coated polyester suture (Ethibond)

3. Pot Life

A pot life study was conducted for Examples 2a, 3a and 4a, together withControl Examples 1a and 2a, by observing changes in viscosity of thesolution. The viscosities of these samples were measured over a periodof 8 hours and the results are summarized in Table 5.

TABLE 5 Viscosity Changes in Coating Solutions Over Time (cPs) Sample 5min 1 hr 4 hr 8 hr Example 2a 2.00 2.25 2.00 2.25 Example 3a 1.50 1.501.50 3.00 Example 4a 7.25 7.00 7.50 7.25 Control Example 1a 7.50 7.257.50 7.75 Control Example 2a 3.50 Gel* *sample ceases to flow after 25minutes.

Example 2a, 3a, 4a and Control Example 1a (which all containing thenovel catalyst of this invention) gives consistent viscosities for up to8 hours, which is suitable for the typical suture coating productioncycle. The Karstedt catalyst (Control Example 2a) is unable to provideconsistent viscosity and gels within 25 minutes, which renders itunsuitable for any meaningful scale suture coating process.

The novel coatings and catalyst of the present invention have manyadvantages compared with the coatings and catalysts of the prior art.The coatings allow for precise control over the crosslinked polymernetwork structure, leading to consistency of the resulting coatings andthe consistency of the performance of coated devices, in particularcoated surgical sutures. The coatings provide a unique polymeric networkstructure, which provides both lubricity and durability of the resultingsilicone coating. The catalyst provides command cured catalytic action,enabling the coating solution to form a film rapidly while possessingdesirably long pot life. The catalyst is inhibited at low or ambienttemperatures and uninhibited or reactivated at temperatures that do notdeform polymeric sutures or other polymeric medical devices. Thecoatings and catalysts provide for more efficient coating and curingprocesses.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

1-15. (canceled)
 16. A composition comprising a platinumdivinyltetramethyldisiloxane vinylcyclohexanol complex having theformula:

.
 17. A coating composition comprising: a cross-linkable siliconepolymer having reactive functionalities; a silica-containingcomposition; a silicone cross-linking agent; and, a catalyst, whereinsaid catalyst is an ambient inactive catalyst and consists essentiallyof platinum divinyltetramethyldisiloxane vinylcyclohexanol complexhaving the formula:

.
 18. The coating composition of claim 17, wherein the composition iscurable at temperatures from about 70 C and higher.
 19. The coatingcomposition of claim 18, wherein the composition is curable attemperatures of about 95 C in about 2 minutes.
 20. The coatingcomposition of claim 17, wherein the cross-linkable silicone polymer isselected from the group consisting of vinyl terminatedpolydialkylsiloxane, vinyl terminated polydimethylsiloxane, vinylterminated polydiphenylsilane-dimethylsiloxane copolymer, vinylterminated polyphenylmethylsiloxane, vinyl terminatedpolyfluoropropylmethyl-dimethylsiloxane copolymer and vinyl terminatedpolydiethylsiloxane.
 21. The coating composition of claim 17, whereinthe cross-linkable silicone polymer comprises vinyl terminatedpolydimethylsiloxane.
 22. The coating composition of claim 17, whereinthe silica-containing composition comprises a trimethyl silyl surfacetreated silica filler.
 23. The coating composition of claim 17, whereinthe silica-containing composition is selected from the commerciallyavailable reactive silica-containing silicone bases including HCR (highconsistent rubber) bases and LSR (liquid silicone rubber) bases.
 24. Thecoating composition of claim 23, wherein the silica-containingcomposition is a liquid silicone rubber base.
 25. The coatingcomposition of claim 17, wherein the silicone cross-linking agent isselected from the group consisting of polymethylhydrosiloxane,polymethylhydro-co-polydimethylsiloxane, polyethylhydrosiloxane,polymethylhydrosiloxane-co-octylmethylsiloxane, andpolymethylhydrosiloxane-co-methylphenylsiloxane.
 26. The coatingcomposition of claim 17, wherein the silicone cross-linking agentcomprises polymethylhydrosiloxane.
 27. The coating composition of claim17, wherein the coating composition additionally comprises about 75 wt.% to about 93 wt. % of an organic solvent, based upon the weight of thecoating composition.
 28. The coating composition of claim 17, whereinthe coating composition comprises about 0.2 wt. % to about 6 wt. % ofthe silicone cross-linking agent based on total solids, wherein thecoating composition additionally comprises about 75 wt. % to about 93wt. % of an organic solvent, based upon the weight of the coatingcomposition.
 29. The coating composition of claim 17, wherein thecoating composition comprises about 0.0004 wt. % to about 0.0036 wt. %of the platinum catalyst, based on total solids, wherein the coatingcomposition additionally comprises about 75 wt. % to about 99.5 wt. % ofan organic solvent, based upon the weight of the coating composition.30. The coating composition of claim 17, wherein the coating compositionadditionally comprises a solvent selected from the group consisting ofxylene, toluene, pentane, hexane, heptanes, octane, mixtures of highermolecular weight olefins, and combinations thereof.